1. Field of the Invention
The present invention relates to an image reading device, and more specifically, to a thin image reading device.
2. Description of the Prior Art
In the modern age, it is important to make electronic products more compact in size. For a scanner, which scans documents and pictures, the major obstacle to compactness is the size of the scanning module. The design of the scanning module is greatly influenced by the optical path and corresponding reflector installation of the scanning module. In particular, the thickness of the scanning module is closely related to the thickness of the reflectors and their subsequent position and installation. One option to reduce the size of the scanning module is to reduce the thickness of the reflectors. However, if the reflectors are not thick enough, they may be too fragile for use, meaning that they could be broken due to collision, and thus worsening the quality of scanning. Therefore, changing the position and the installation of the reflectors is a preferable manner.
Please refer to FIG. 1 showing the optical path of a conventional scanning module 10 using four reflectors. The scanning module 10 includes a housing 12, a lens 14 for focusing light, a photosensor 16 for converting light from the lens 14 into digital signals, and four reflectors a first reflector 18, a second reflector 20, a third reflector 22 and a fourth reflector 24. The first reflector 18, the second reflector 20, and the fourth reflector 24 are installed on a first side of the lens 14, and the third reflector 22 is installed above the lens 14 on a second side.
When scanning a document, the light is reflected by the document through a slit 26 off the first reflector 18, then the second reflector 20, then the third reflector 22, then the fourth reflector 24, and finally through the lens 14 where it is focused on the photosensor 16, which converts the light into digital signals. As shown in FIG. 1, the first reflector 18, the second reflector 20, and the fourth reflector 24 are installed on the first side of the lens 14, and the third reflector 22 is installed on the second side of the lens 14. Since the third reflector 22 is installed on the opposite side of the first reflector 18, the second reflector 20, and the fourth reflector 24; it needs to be installed above the lens 14 to prevent the lens 14 from interfering with the light reflected from the second reflector 20 to the third reflector 22 and the light reflected from the third reflector 22 to the fourth reflector 24. Because the third reflector 22 is installed above the lens 14, the housing 12 of the scanning module 10 has a height at least equal to the height of the third reflector 22 plus the height of the lens 14.
Therefore, the height of the scanning module 10 can be only reduced in a limited fashion according to the prior art meaning that the thickness of the scanning module can hardly be reduced if the using the conventional installation of reflectors.